Blower damper



1963 J. GOETTL ETAL I 3,

BLOWER DAMPER Filed March 30, 1961 1 2 Sheets-Sheet l INVENTOR.

. JOHN GOETTL M BY ALBERT B. GOETTL 38 ROBERT L. KOBLE JR.

P AT ENT AGENT Dec. 24, 1963 J. GOETTL ETAL 3,115,299

' BLOWER DAMPER Filed March so, 1961 2 Sheets-Sheet 2 INVENTOR.

JOHNGQETTL ALBERT a. GOETTL BY ROBERT L. KOBLE JR PATENT AGENT UnitedStates Patent 3,115,299 BLOWER DAMPER John Goettl, Albert E. Goettl, andRobert L. Koble, In, Phoenix, Ariz., assignors to McGraw-Edison Company,Milwaukee, Win, a corporation of Delaware Filed Mar. 30, 1961, Ser. No.99,480 14 Claims. (Cl. 230-114) This invention relates to a blowerdamper and more particularly to a blower damper wherein the shutolfdamper forms part of a centrifugal blower housing or is directlyconnected thereto to form a very compact damper structure.

Prior art blower outlet control dampers have been installed downstreamof the outlets of centrifugal blowers to control the air flow therefrom.These blower outlet control dampers have been used downstream of theblower outlets of evaporative coolers and other air conditioningequipment as well as for the general control of and or shutolf of flowfrom the outlets of centrifugal blowers.

In evaporative coolers, for example, shutolf dampers have been placed inthe outlet ducts of blowers to shutoff communication of such blowerswith ducts communicating therewith. Such dampers have been conventionalslide type shutoif dampers used during various seasons of the year forshutting off communication of the air conditioning ducts with anevaporative cooler blower. In many instances these dampers prevent theescape of hot air from the ducts through the evaporative cooler blowerduring the winter time and such dampers may be opened during the summertime to permit flow of cool air from the evaporative cooler blower intothe ducts.

In many locations such shutoff dampers are difficult to operate orinstall and in such confined structures as evaporative coolersconventional blower shut off dampers cannot be conveniently installeddue to space limitations.

In evaporative coolers the blower housing structure is ordinarilysurrounded by adjacent walls or evaporative cooler pads and there is notsuflicient room between the blower and the walls or pads to accommodatethe retraction of a damper of sufiiceint cross-sectional area tocompletely shutoff or cover the blower outlet opening.

Accordingly, it is an object of the invention to provide a blower outletdamper mechanism which is adapted to shutoff or vary the blower outletarea of a blower and wherein this damper mechanism is adapted to followor substantially conform to the curvature of the blower housing so thatit is very compact and readily operable within confined spaces where ablower may be installed.

Another object of the invention is to provide a blower outlet dampermechanism which is slidable around the curved wall or portion of acentrifugal blower and project- -ab1e across the outlet opening of acentrifugal blower to shutoff and or control the flow from the blower.

Another object of the invention is to provide a blower damper which isslidable about a curved portion of a centrifugal blower housing andforms a portion of the curved wall thereof whereby the damper whenslidably moved around the curved portion of the blower housing andprojected across the blower outlet opening to close the same, providesan access opening in the curved wall of the blower housing so that theblower wheel internally of the housing may be readily cleaned orserviced through said access opening.

Another object of the invention is to provide a blower damper havingvery compact mechanism operable within confined space internally of theevaporative coolers or the like.

Another object of the invention is to provide a blower damper comprisinga flexible sheet of material adapted 3,115,299 Patented Dec. 24, 1963 toslide around the curvature of a blower housing and having an inner edgenormally disposed to serve as a blower cutoll when said damper isv inopen position and projectable to shutofl the outlet of said blower whensaid damper is in closed position.

Another object of the invention is to provide a blower damper having aflexible plate slidable around a curved side wall of a centrifugalblower and projectable into the outlet of said blower for shutting offthe fiow therefrom whereby slidable movement of said plate exposes anopen area in the curved side wall of the blower housing and wherebyanother flexible curved plate is slidable in the opposite directionaround said housing to expose an additional opening in the curved blowerhousing so that the combined opening exposed by both of said plates issulficient to permit removal of the blower wheel from the housingthrough the combined opening.

Another object of the invention is to provide a blower outlet damperusable in connection with centrifugal blowers wherein the damper is aflexible plate slidable around the curved surface of a centrifugalblower and having an inner edge project-able across the outlet openingof the blower; said damper member having a gear rack means thereon; anda spur gear mechanism meshing with said rack means and disposed toacutate said damper into and out of closed position with respect to theoutlet opening of said blower.

Further objects and advantages of the invention may be apparent from thefollowing specification, appended claims and accompanying drawings inwhich:

FIG. 1 is a side elevational view of an evaporative cooler showing ablower therein and installed on the roof of a building and showingportions broken away and in section to amplify the illustration;

FIG. 2 is a fragmentary sectional view taken from the line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken from the line -33of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view taken from the line 4-4of FIG. 2;

FIG. 5 is a fragmentary sectional view taken from the line 55 of FIG. 4;

FIG. 6 is a fragmentary sectional View taken cfrom the line 66 of FIG.4;

FIG. 7 is a fragmentary side elevational view of a modified form of theinvention showing a blower and blower damper and portions of the blowerhousing in section and illustrating by arrows the direction of movementof the damper about the curved structure of the blower housing;

FIG. 8 is a fragmentary sectional view taken from the line 3-8 of FIG.7;

FIG. 9 is a view similar to FIG. 7 but showing a further modified formof the blower damper in accordance with the present invention;

FIG. 10 is another view similar to FIG. 7 but showing an additionalmodification of the invention;

FIG. 11 is another view similar to FIG. 7 showing a further modificationon an enlarged scale and illustrating a rack and pinion mechanism formovement of the damper with respect to the blower housing; and

FIG. 12 is a fragmentary sectional view taken from the line 12-12 ofFIG. 11.

As shown in FIG. 1 of the drawings, the blower damper of the inventionis disclosed in connection with a blower internally of an evaporativecooler which is located on the roof of a building. The damper of thepresent invention is thus disclosed to illustrate one advantageousinstallation application thereof.

As shown in FIG. 1, an evaporative cooler 14 is mounted on a buildingroof 16 having a duct 18 extending upwardly therethrough to the outlet20 of a blower 22 is internally of the evaporative cooler 14. Theevaporative cooler 14 is provided with side walls 24 having evaporativecooler pads 26 therein. These evaporative cooler pads 26 are closelyadjacent the blower 22 and normally there is not sufficient distancebetween the extremities of the outlet 20 and any one of the evaporativecooler pads 26 for slidably actuating a conventional damper to shut offthe outlet 26 of the blower 22. This blower 22 is a conventionalcentrifugal blower having the usual eccentrically mounted rotor 28therein discharging through a substantially tangential outlet 20 of theblower housing.

Conventional centrifugal blowers of this type are usually provided witha flow cutoff normally located at 3i). This structure at 34 shown inFIG. 1 of the drawings is a rolled edge 32 of a shutoff damper accordingto the present invention. This rolled edge 32 serves two purposes,namely as a blower cutofl and as a shutoff edge of a slidable dampermember 34 which is disposed to shutoff the blower outlet Ztl and preventflow outwardly from the blower in the direction of the arrows A in FIG.1 of the drawings. As shown in FIGS. 1 and 5 of the drawings, the dampermember 34 is a thin flexible sheet of metal having its opposite edgesdisposed in channel shaped guides on guide channels 36 supported onopposite inner side walls of the blower outlet 20. These guide channels36 support opposite edges 38 of the damper member 34 so that the dampermember 34 may be transformed from an arcuate shape to a straight flatshape when moved from open position as shown by solid lines in FIG. 1 toa damper closed position shown by broken lines in FIG. 1.

As shown in FIGS. 1 and 6 of the drawings, opposite side walls 46 of theblower housing are provided with inwardly directed flanges 42 formingguides extending inwardly of the opposite edges 33 of the damper member34 so that the damper member 34- when in the solid line position shownin FIG. 1 of the drawings is retained in a curved or arcuate shapeadjacent the arcuate or curved flanges 42 which are integral with theopposite side walls 40 of the blower housing.

Inwardly of the damper member 34 adjacent the curved flanges 42 areannular in cross section guide spools 44 held to the side walls 40 bymeans of screws 46. These guide spools 44 may be made of nylon or othersuitable material and their peripheral portions are slightly spaced fromthe inwardly directed flanges 42 so that the damper member 34 may bedisposed between the guide spools 44 and the guide flanges 42. Thus, thedamper 34!- is provided with a guide means at its op osite endsincluding the curved flanges 42 and corresponding guide spools 4d. Thedamper member 3 5 at its edge opposite to the rolled edge 32 is providedwith a clip edge 48 which is substantially channel shaped in crosssection. This clip edge 48 is retained in a clip detent which isintegral with an arcuate or curved wall 52 of the blower housing.

As shown in detail in FIG. 3 of the drawings, the clip edge 48 isretained and held by the clip detent portion d of the curved wallportion 52 of the blower housing and it will be understood that the clipdetent St is resilient so that it may be sprung outwardly in thedirection of the arrow B in FIG. 3 of the drawings to permit a releaseof the clip 43 therefrom so that the damper member 34 may be moved inthe direction of the arrow C in FIG. 3 of the drawings.

A cup shaped recess member 54 is located in the damper member 34 and itis spot welded thereto providing a recess in which a person may placehis fingers to apply force to the damper member in the direction of thearrow C or in the opposite direction depending upon whether it isdesired to move the damper to closed or open positions, respectively.

As shown in FIGS. 4 and 5 of the drawings, the duct 18 is provided witha conventional outwardly extending flange 56 surrounded by a resilientgasket 58 the upper surface of which is engaged by a flange tillsurrounding the outlet of the blower. Clips 62 are folded under a lowerportion 64 of the gasket 58 to retain the blower housing securelyconnected in sealed relationship with the flange 56 of the duct 18.

As shown in FIG. 1 of the drawings, it will be seen that duringoperation of the blower 22 the damper 34 may be maintained in the solidline position for a normal blower operation wherein the curled edge 32,of the damper 34 acts as conventional blower cutoff at the outletthereof.

When it is desired to shut ofl or partially shut oil the outlet of theblower the detent clip 50 may be sprung outwardly in the direction ofthe arrow B while force is exerted in the recess 54 of the damper member34 in the direction of the arrow C until the clip portion 43 is releasedfrom the detent clip Sil. The damper 34 is then slidably projectedaround the inner surfaces of the guide flanges 42 hereinbefore describedand inwardly of the guide spools 4-4 until the rolled edge 32 isprojected to a desired position either to partially close the outlet 2of the blower or completely to close the outlet of the blower asindicated by broken lines D. The roller edge 32 of the damper member 34when engaged with the outlet side wall 33 completely closes the outletZil.

It will be appreciated that the hereinbefore described channel members36 at opposite sides 4% of the blower housing are straight and disposedsubstantiall tangentially of the curved portion of the damper and/ or acurved wall of the blower housing and tend to transform the dampermember 34 from a curved disposition, as shown by solid lines, to astraight disposition as shown by broken lines in FIG. 1 of the drawings.

It will be understood that this damper member 34 is preferably offlexible and or resilient material capable of being deflected intoconforming relationship with curvature of the blower housing whereby theretraction of the damper member 34 into an open damper position does notinterfere with the side walls of an evaporative cooler or any othersurrounding structure but merely follows the curvature of the blowerhousing side wall and thereby provides a blower damper which is capableof fully shutting oil the entire cross sectional area of the bloweroutlet without consuming substantially more space than the blower itselfoccupies.

In the modification as shown in FIG. 7 of the drawings, the dampermember 34 at its curled edge 32 is structurally similar to that shown inFIG. 1 of the drawings, however, the damper member 34 as shown in FIG. 7of the drawings, is provided with a handle 66 which is fixed thereto andwhich projects outwardly through a slot 68 in the curved wall or portion52 of the blower housing. Thus, when the handle as is projected from thesolid line position, shown in FlGS. 7 and 8 to the broken line positionshown therein, the damper member 34 is projected from an open damperposition into a closed damper position.

Guide spools 44 are provide to guide the damper member 34 while guidechannels 38, similar to the guide chan nels 38 shown in FIG. 5 of thedrawings, are provided to guide opposite edges of the damper member 34into a straight line condition across the outlet of the blower 22.

It will be seen that the damper member 34 as shown in FIG. 7 of thedrawing, is disposed inwardly of the arcuate wall or portion 5 2 of theblower housing.

Actually the wall 52 may be arcuate or may be an irregularly curvedshape, however, for all practical purposes of description this wall willbe referred to as a substantial arcuate or curved wall. Thus, it will beunderstood that the wall 52 provides a curved guide for the dampermember 34 at its outer surface and different from the damper 34 shown inFIG. 1 in that the structure shown in FIG. 1 utilizes the curved flanges42 to provide an outer support for the damper 34.

In the modification as shown in FIG. 9, the blower 22 is provided with aconventional blower cutofi 7t and a damper structure 72 is operableseparately from the cutoff structure '70. This damper "72 is a sheet offlexible metal or other equivalent material and when in open position isdisposed in curved form around the curved wall 52 of the blower housing22, and when in closed position is projected across the entire crosssectional area of the blower outlet 29 in a similar manner to thedisposition of the damper 34 shown in FIGS. 1 and 7 of the drawings.

This damper 72 at its opposite edges is supported in guide channels 38secured to opposite inner side Walls of the blower housing ashereinbefore described. The damper member 72 adjacent the cunved wall52. of the blower housing is supported in curved guide channels 74 whichare secured by spot welding 75 to opposite sides 4% of the blowerhousing.

It will be seen that the damper member 72 is provided with an inner edge76 which corresponds to the rolled edge 32 of the damper member 34. Thisedge 76 when disposed adjacent the wall 33 of the blower housingprovides for complete shutoif of the flow outwardly through the bloweroutlet 2%. When the edge 76 is adjacent the wall 33 a damper actuatinghandle 78 is disposed in a broken line position F all as shown best inFIG. 9 of the drawings.

In the modification as shown in FIG. 10 of the drawings, the structureof the damper 34 is identical to that as shown in FIG. 1 of thedrawings, however, the clip detent St is integral with a curved slidingsection Sit of the blower housing. This section 89 replaces a shortsection of the curved side wall 52 whereby the section 80 is slidable toa broken line position G. Thus, the section 89 when moved to the brokenline position G, and the damper 34 when moved to the broken lineposition as shown in FIG. 1 of the drawings, exposes a combined openingin the side of the blower housing sufliciently large for the removal ofthe blower wheel.

The section 84) is guided internally of the curved wall 52 of the blowerhousing by guide spools 44 secured to the end walls 4% of the blowerhousing in a similar manner to the guidance of the damper member 34shown in FIG. 1 of the drawings.

It will be understood that operation of all of the dampers 34 and 72, asdisclosed herein, may expose an opening in the side wall of the curvedwall or curved portion of the blower housing when these dampers are inshut off position whereby, access to the blower may be had through theopening in the arcuate wall of the housing in order to clean the blowerwheel without the necessity of removing it from the blower housing.

In the modification as shown in FIGS. 11 and 12 of the drawings, ablower damper member 82 is provided with corrugated gear rack portions84 at its opposite edges with which pinion gears 86 mesh. These piniongears 86 are mounted on shafts 88 supported in bearings 90 secured tothe side wall portions 40 of the blower housing. Secured to these shafts88 are handles 92 which are provided for rotation of the shafts 88together with the pinions 86 to move the corrugated rack portions 84 andthe damper member 82 slidably around the curved side wall portion 2 ofthe housing as hereinbefore described.

It will be appreciated that the damper 82 may be supported and guided ina manner similar to the hereinbefore described damper 34 and thatvarious means may be substituted for the handle 92, for example, anypower means may be connected thereto for actuating the damper 82.

The damper 82, as shown in FIGS. 11 and 12, it supported at itsoutermost corrugated rack edges by the flanges 42 integral with the sidewalls 4%} of the blower housing and guide spools 44 operate to supportthis damper member 82 in a similar fashion to the operation of the guidespools 44 adjacent the damper member 34.

It will be obvious to those skilled in the art that variousmodifications of the present invention may be resorted to in a mannerlimited only by a just interpretation of the following claims.

We claim:

1. In a blower damper the combination of: a blower housing; a blowerrotor therein; an outlet portion of said blower housing disposed toconduct flow from said rotor; a flexible damper means disposed slidablyacross said outlet portion of said blower and adapted to shut ofl? flowtherethrough; a curved portion of said blower housing adjacent saidoutlet portion; a portion of said flexible damper means disposed insubstantially curved conformity with said curved portion of saidhousing; and substantially straight guide means disposed substantiallytangentially with respect to said curved portion of said blower housingto guide the movement of said flexible damper means across said outletportion of said blower; and to guide said portion of said flexibledamper means around the curved portion of said blower housing, saidcurved portion of said blower housing having an opening therein; saidportion of said flexible damper disposed to expose said opening whensaid flexible damper is projected across the outlet portion of saidblower housing, said portion of said damper means being disposed toclose said opening in said curved portion of said blower housing whensaid flexible damper means is retracted out of interference with flowpassing through said outlet portion of said blower housing.

2. In a blower damper the combination of: a blower housing; a blowerrotor therein; an outlet portion of said blower housing disposed toconduct flow from said rotor; a flexible damper means disposed slidablyacross said outlet portion of said blower and adapted to shut off flowtherethrough; a curved portion of said blower housing adjacent saidoutlet portion; a portion of said flexible damper means disposed insubstantially curved conformity with said curved portion of saidhousing; and substantially straight guide means disposed substantiallytangentially with respect to said curved portion of said blower housingto guide the movement of said flexible damper means across said outletportion of said blower; and to guide said portion of said flexibledamper means around the curved portion of said blower housing, saidcurved portion of said blower housing having an opening therein; saidportion of said flexible damper disposed to expose said opening whensaid flexible damper is projected across the outlet portion of saidblower housing, said portion of said damper means being disposed toclose a first portion of said opening in said curved portion of saidblower housing when said flexible damper means is retracted out ofinterference with flow passing through said outlet portion of saidblower housing, said curved portion of said blower housing having acurved wall portion slidably positioned over a second portion of saidopening in said curved portion, said curved wall portion slidable in theopposite direction around said curved portion of said housing :from thesliding direction of said flexible damper means when projected acrosssaid blower housing outlet portion whereby said curved wall and saidflexible damper means may be retracted away from each other around thecurved portion of said blower housing to expose the entire area of saidopening therein providing for access to said rotor and the removal ofthe same through said opening in said curved portion of said blowerhousing.

3. In a blower damper the combination of: a blower housing; a blowerrotor therein; an outlet portion of said blower housing disposed toconduct flow from said rotor; a flexible damper means disposed slidablyacross said outlet portion of said blower and adapted to shut ofl flowtherethrough; a curved portion of said blower housing adjacent saidoutlet portion of said flexible damper means disposed in substantiallycurved conformity with said curved portion of said housing; andsubstantially straight guide means disposed substantially tangent tosaid curved portion of said blower housing and disposed to guide themovement of said flexible damper means across said outlet portion ofsaid blower and to guide said portion of said flexible damper meansaround the curved portion of said blower housing, said curved portion ofsaid blower housing having an opening therein; said portion of saidflexible damper disposed to expose said opening when said flexibledamper is projected across the outlet portion of said blower housing,said portion of said damper means being disposed to close a firstportion of said opening in said curved portion of said blower housingwhen said flexible damper means is retracted out of interference withflow passing through said outlet portion of said blower housing, saidcurved portion of said blower housing having a curved wall portionslidably positioned over a second portion of said opening in said curvedportion, said curved wall portion slidable in the opposite directionaround said curved portion of said housing from the sliding direc tionof said flexible damper means when projected across said blower housingoutlet portion whereby said curved wall and said flexible damper meansmay be retracted away from each other around the curved portion of saidblower housing to expose the entire area of said opening thereinproviding for access to said rotor and the removal of the same throughsaid opening in said curved portion of said blower housing; meansreleasably coupling adjacent portions of said flexible damper means andsaid curved wall portion to retain the same in position to cover saidopening in said curved portion of said blower housing.

4. In a blower damper the combination of: a blower housing; a blowerrotor therein; an outlet portion of said blower housing disposed toconduct flow from said rotor; a flexible damper means disposed slidablyacross said outlet portion of said blower and adapted to shut ofl" flowtherethrough; a curved portion of said blower housing adjacent saidoutlet portion; a portion of said flexible damper means disposed insubstantially curved conformity with said curved portion of saidhousing; and substantially straight guide means disposed substantiallytangentially with respect to said curved portion of said blower housingto guide the movement of said flexible damper means in progressing froma flat configuration toward a relatively curved configuration in movingacross said outlet portion of said blower; and further guide structuredisposed to guide said portion of said flexible damper means around saidcurved portion of said blower housing; said damper operable relative tosaid guide means and projectable along said damper guide means acrossthe area of said outlet to a closed shut off position to shut off flowtherethrough; and an edge portion of said damper disposed at said bloweroutlet and, said edge when retracted out of closed shut off positiondisposed and serving as a blower cut off.

5. A centrifugal blower having a volute housing and an outlet port insaid housing, said port being in a plane substantially tangent to saidhousing, said volute housing having at least one axially located inlet,a rotor mounted in said housing and adapted to draw fluid through saidinlet and move said fluid centrifugally through said port, a flexibledamper disposed to be moved across said port and having a portion to beflexibly curved to conform to said housing curvature and a portionextending from said curved portion to be flexed into generally flatconfiguration in being moved across said port, means for guiding saiddamper from curved to flat condition in moving across said port in saidgenerally fiat configuration.

6. A blower as set forth in claim 5, said flexible damper having an edgemovable into the fluid flow from said rotor as said damper is movedacross said port, so as to divide said flow into a predetermineddischarge portion through said port and into a portion for recirculationby said rotor, said flexible damper being movable to an extent to fullyshut off said port from discharge.

7. A blower as set forth in claim 5, said guide means comprisingstraight and curved portions for guiding said flexible damper from acurved condition to a relatively flatter condition in moving across saidport, said curved portion being within said housing and said straightportion being generally coplanar with said port, one end portion of saidflexible damper being curved to conform with the curvature of saidhousing at all times and another end portion being in relatively flattercondition at all times.

8. A blower as set forth in claim 5, said damper having an edge disposedto move in a plane generally tangent to the volute housing atsubstantially least radius of said housing with respect to the axis ofsaid rotor.

9. In a blower damper the combination of: a blower housing; a blowerrotor therein; an outlet portion of said blower housing disposed toconduct flow from said rotor; a flexible damper means disposed slidablyacross said outlet portion of said blower and adapted to shut off flowtherethrough; a curved portion of said blower housing adjacent saidoutlet portion; a portion of said flexible damper means disposed insubstantially curved conformity with said curved portion of saidhousing; substantially straight guide means disposed substantiallytangentially with respect to said curved portion of said blower housingto guide the movement of said flexible damper means across said outletportion of said blower; and curved guide structure to guide said portionof said flexible damper means around the curved portion of said blowerhousing; said flexible damper having an edge portion forming a flowcut-ofl adjacent said rotor.

10. A centrifugal blower as set forth in claim 5, said housing having aslot and a handle element extending therethrough and secured to saiddamper whereby said damper may be moved by means of said handle acrosssaid port.

11. A centrifugal blower as set forth in claim 5, said damper beingprovided with corrugations, and a gear carried by said housing andmounted for rotation to drive said damper across said port.

12. A centrifugal blower as set forth in'claim 5, said damper beingdisposed on the exterior of said housing and said housing having anopening adjacent said port through which a portion of said damperextends.

13. A centrifugal blower as set forth in claim 5, said housing having anopening in the side thereof sufficiently large for removal of the rotortherethrough and having a closure section for said opening, and meansfor slidably guiding said closure section with respect to said housingto partially expose said opening, and means for removably securing saidsection to said damper whereby said section and said damper togetherfully close said opening but may be separated and moved in oppositedirections to substantially fully expose said opening.

14. A centrifugal blower as set forth in claim 5, said damper forming aportion of the wall of sad housing when said port is open and effectingan opening in said wall in moving toward closure of said port.

References Cited in the file of this patent UNITED STATES PATENTS284,279 Cockson Sept. 4, 1883 823,637 Prame June 19, 1906- 829404 KimeAug. 28, 1906 874,329 Gray Dec. 17, 1907 2,298,745 Klockau Oct. 13, 19422,316,224 DElia Apr. 13, 1943 2,656,095 Campbell Oct. 20, 1953 FOREIGNPATENTS 26,130 Great Britain Nov. 19, 1906 65,083 Denmark Nov. 18, 1946

1. IN A BLOWER DAMPER THE COMBINATION OF: A BLOWER HOUSING: A BLOWERROTOR THEREIN; AN OUTLET PORTION OF SAID BLOWER HOUSING DISPOSED TOCONDUCT FLOW FROM SAID ROTOR; A FLEXIBLE DAMPER MEANS DISPOSED SLIDABLYACROSS SAID OUTLET PORTION OF SAID BLOWER AND ADAPTED TO SHUT OFF FLOWTHERETHROUGH; A CURVED PORTION OF SAID BLOWER HOUSING ADJACENT SAIDOUTLET PORTION; A PORTION OF SAID FLEXIBLE DAMPER MEANS DISPOSED INSUBSTANTIALLY CURVED CONFORMITY WITH SAID CURVED PORTION OF SAIDHOUSING; AND SUBSTANTIALLY STRAIGHT GUIDE MEANS DISPOSED SUBSTANTIALLYTANGENTIALLY WITH RESPECT TO SAID CURVED PORTION OF SAID BLOWER HOUSINGTO GUIDE THE MOVEMENT OF SAID FLEXIBLE DAMPER MEANS ACROSS SAID OUTLETPORTION OF SAID BLOWER; AND TO GUIDE SAID PORTION OF SAID FLEXIBLEDAMPER MEANS AROUND THE CURVED PORTION OF SAID BLOWER HOUSING, SAIDCURVED PORTION OF SAID BLOWER HOUSING HAVING AN OPENING THEREIN; SAIDPORTION OF SAID FLEXIBLE DAMPER DISPOSED TO EXPOSE SAID OPENING WHENSAID FLEXIBLE DAMPER IS PROJECTED ACROSS THE OUTLET PORTION OF SAIDBLOWER HOUSING, SAID PORTION OF SAID DAMPER MEANS BEING DISPOSED TOCLOSE SAID OPENING IN SAID CURVED PORTION OF SAID BLOWER HOUSING WHENSAID FLEXIBLE DAMPER MEANS IS RETRACTED OUT OF INTERFERENCE WITH FLOWPASSING THROUGH SAID OUTLET PORTION OF SAID BLOWER HOUSING.